Cerebral palsy is a non-progressive, permanent syndrome that occurs in childhood and is accompanied by motor, tônus and posture disorders. Its etiology is related to an insult or damage to the central nervous system in maturation. Approximately 80% of cerebral palsy course with spasticity, which, when left untreated, will generate pain and functional, anatomical and structural changes, with a negative impact. Photobiomodulation therapy has biological effects of tissue regeneration, muscle relaxation, vasodilation, reduction of the inflammatory process and relief of pain symptoms already described in the literature, in addition to being feasible, practical, safe, without side effects, painless and non-invasive.This study is a blind, randomized and controlled clinical trial that will evaluate the effect of photobiomodulation in reducing gastrocnemius muscle spasticity in children aged 2 to 18 years, diagnosed with spastic cerebral palsy of lower limbs of any etiology for at least 03 months and randomized into two groups: application of Low Intensity LED Therapy in the medial and right lateral gastrocnemius muscles (device power of 100mW, wavelength of 850nm, energy of 3J/cm2/point, once a week, making 08 therapeutic days during 02 months) or placebo group Low-Intensity LED Therapy (same device turned off). Both groups will also receive the standard treatment for spasticity. To assess the response to therapy, the outcomes evaluated will be the modified Ashworth Scale, the Mobility Domain of Pediatric evaluation of disability inventory, the Gross Motor Function Classification System scale and passive and active range of motion of the ankle analyzed at the pré and post each therapeutic session and in the pre and post therapeutic period of 08 sessions.